This invention relates to a cylinder sleeve for a reciprocating machine such as a two-cycle engine and more particularly to an improved cylinder sleeve and method manufacturing it for such machines.
In many forms of reciprocating machines, such as internal combustion engines, a cylinder liner is employed that is pressed or otherwise secured within a cylinder block. Such constructions are frequently employed so as to permit the use of lightweight cylinder block materials with a more rigid wear resistant material being utilized to form the actual cylinder liner. Frequently it is also the practice to form the cylinder liner with a plating wear resistant coating on its inner surface so as to further improve the longevity and performance of the machine.
In connection with such machines, particularly those operating on a two-stroke principal, it has been the practice to form one or more ports that extend through the cylinder liner and which cooperate with matching ports in the cylinder block material. Where the cylinder liner is plated and has ports, this can present certain problems as may be best understood by reference to FIG. 1 which is a showing of a cylinder liner, indicated generally by the reference numeral 12 in which a scavenge port 13 and exhaust port 14 are formed. The cylinder liner 12 is comprised of a base material 15 such as an aluminum alloy on which a wear resistant coating 16 is plated. The coating may be silicone or a silicone alloy or the like.
As may be readily seen from FIG. 1, the plating process tends to cause an extending portion of the plating material 16 to extend through and beyond the periphery of the scavenge and exhaust ports 13 and 14. This extending material is indicated by the reference numerals 16a and 16b. Hence, when the cylinder liner 12 has its outer peripheral surface machined, as by turning using a cutting tool 17, the leading portion of the plating 16a and 16b will be tend to be torn away from the base material 15. This will occur even if the plating material does not extend beyond the outer periphery of the respective ports 13 and 14.
One way in which it has been proposed to eliminate the aforenoted problem, is by using a jig or fixture 18 as seen in FIG. 2, which is put in place during the plating process so that the plating 16 will not extend to the finish diameter D of the finished material. Of course, this necessitates the use of special jigs during the plating process and can increase the cost. In addition, it may not be possible to fully insure that the plating will be stopped beyond the portion of the port internally of the finished diameter D. Another method is to employ a protective or stop coating 19 during the plating process which then must be removed subsequently as shown in FIG. 3.
Even if the two methods previously described are employed and are successful, certain problems still exist when the cylinder liner 12 is positioned in the cylinder block as may be best understood by reference to FIG. 4. In this figure, the cylinder block is indicated by the reference numeral 21 and it will be noted that is has a scavenge port 22 that cooperates with the corresponding port 13 formed in the liner 12 and an exhaust port 23 that cooperates with the liner exhaust port 14. It will be seen that the resulting construction leaves shoulders that are exposed to and can interfere with the gas flows through these ports. In addition, these shoulders themselves offer surfaces against which the flow can impact and cause erosion or stripping of the plating material 16.
It is, therefore, a principal object of this invention to provide an improved plated cylinder liner for a reciprocating machine and method of manufacturing it that will not have the disadvantages as aforenoted.
Specifically, it is an object of this invention to provide a method for making a plated liner and such a liner wherein the plating will not tend to abrade, wear off or interfere with the flow in ultimate use.
It is a still further object of this invention to provide an improved method for manufacturing a plated port for a cylinder liner and a port configuration therefore.